Not sure what you are asking? It’s programmable - means it doesn’t work just one way!

Additional reading:
KeyOff XA CONTROL

Bad Mister, thank you!
In slowly tempo I missed odd beat.
1beat Normal, 2beat KeyOff
3beat Normal, 4beat KeyOff etc.
KeyOff layer skips

I have two independent elements: strum down and strum up

No problem, but very slow tempo may be missed second strike

This may not explain everything, but there's a way to link the key off's amplitude to the tail end of the key on sample's amplitude envelope at the time you switch. Therefore, if you let go of a key after the key-on sample has reached the final decay of the envelope (and at this point the level is "0" for the envelope) - then the key off sample will start off at 0 -- where the key on sample left off. EDIT: adding: this mechanism involves having the key off sample in the same element GROUP as the key on sample. This is how the key off sample will match the level of the key on sample - wherever it leaves off.

There's also a way to do this differently (by not grouping the key off element in a group). I know because sometimes I've seen the key off amplitude can always start with the original key-on velocity regardless of where the key-on sample is in its envelope.

What I'm not sure about is the case where the key-on sample does not loop and it reaches the end of the sample altogether. It's possible that the system would elect not to play a key-off sample although I'm not sure and would need to do an experiment. If this is the the case (not sure) then my fix would be to edit the sample to sample in "silence" so the sample will play "silence" past the point where the sample currently ends. This way I could play a percussive sound like a guitar which would decay quickly possibly and have "silence" but the sample is still "running" playing my fake silence in the new sample. And when I let go - it will be from an actively playing sample.

I then remembered another option that a three-beat rhythm may be needed.
Probably have to go back to the velocity mode instead XA Control.
It's a pity that there is no double KeyOff. (KeyOff after KeyOff)
Waltz - one two three, one two three...
1 beat – velocity layer (0–79)
2 beat – velocity layer (80–127)
3 beat – maybe Key Off 🙂 or velocity layer (80–127)

To do the A-B-B pattern I think you're going to need to abandon complete control using key on and key off and instead use an ARP that plays the 3 beats (Layer A, Layer B, Layer B). You lose the control over speed of the 3 notes - but that would pretty much be how this needs to be done.

Also - even note on/off "strumming" I find difficult because of syncopation vs non. I don't always want to end on the beat where my hand is "off" the keys -- which is natural. Having to hold the keys down in order not to trigger the key off sample is not something I've been willing to deal with. I think the key on+off strumming is best for a fast strum where it doesn't matter if you always end with the note off. Worse for slower strumming where every strum (note on or note off) requires precise placement.